CORRELATION OF HIGH-TEMPERATURE STABILITY OF ALPHA-CHYMOTRYPSIN WITH SALTING-IN PROPERTIES OF SOLUTION

A correlation between the stability of alpha-chymotrypsin against irre versible thermal inactivation at high temperatures (long-term stabilit y) and the coefficient of Setchenov equation as a measure of salting-i n/out efficiency of solutes in the Hofmeister series has been found. A n increase in the concentration of salting-in solutes (KSCN, urea, gua nidinium chloride, formamide) leads to a many-fold decrease of the ina ctivation rate of the enzyme. In contrast, addition of salting-out sol utes has a small effect on the long-term stability of alpha-chymokypsi n at high temperatures. The effects of solutes are additive with respe ct to their salting-in/out capacities; the stabilizing action of the s olutes is determined by the calculated Setchenov coefficient of soluti on. The correlation is explained by a solute-driven shift of the confo rmational equilibrium between the 'low-temperature' native and the 'hi gh-temperature' denatured forms of the enzyme within the range of the kinetic scheme put forward in the preceding paper in this journal: irr eversible inactivation of the high-temperature form proceeds much more slowly compared with the low-temperature form.